Liverpool Telescope frame of the AGN 0957+561 on 5th December 2011. This typical 120 second exposure in SDSS-R band shows the two images of the gravitationally lensed AGN, which are separated by ~6 arcsec (marked with
a blue arrow).

A long-term photometric monitoring study with the Liverpool Telescope (LT)
was recently used to unveil the nature of the accretion flow and jet
connection of a distant active galactic nucleus (AGN) for the first time.
This project was conducted by the
GLENDAMA research team (Rodrigo
Gil-Merino, Luis J. Goicoechea, Vyacheslav Shalyapin and Vittorio F.
Braga) at the Universidad de Cantabria (Spain), and the LT has been the key facility to carry it out.

AGNs generate spectacular X-ray, ultraviolet (UV) and optical continuum
luminosities by matter accretion onto their central rotating supermassive
black holes. However, the precise geometry and origin of this huge energy
production is still largely unknown, and direct spatial resolution of the
emitting regions from such objects is not currently possible. Fortunately,
there is a time-domain technique to probe the accretion physics for AGNs.
This is the so-called "continuum reverberation" (or echo) mapping, which
relies on the analysis of time-delayed responses of different continuum
emitting regions to original fluctuations in a driving source.

A successful reverberation analysis requires multiwavelength monitoring
during a period of strong variability. At redshifts z > 1, this task is
much easier to plan for a gravitationally lensed AGN (the gravitational
field of foreground galaxies produces two or more images of the same
background galaxy nucleus), since the variability of some of its multiple
images can be predicted in advance based on an optical follow-up of the
lens system on a nightly basis. The double-image AGN 0957+561 (designation
based on its position in the sky) is located at a luminosity distance from
Earth of ∼33 thousand million light years (z = 1.41), and it was
intensively monitored with the LT between 2005 and 2010. As intrinsic flux
variations in the image 0957+561B lag those in the image 0957+561A by
about 14 months, the LT detection of significant flux variations in
0957+561A between late 2008 and mid-2009 allowed the GLENDAMA team to
organize a multiwavelength follow-up campaign during the first semester of
2010. This included observations with two NASA satellites: Chandra X-ray Observatory and
Swift, supported by the LT in the
Sloan "griz" passbands.

The X-ray, UV and optical brightness records of 0957+561B in 2010
confirmed its intrinsic origin and led to a reverberation mapping of the
continuum sources in the distant AGN. For example, the UV-optical fluxes
in the Ugr passbands were used to detect interband delays of several
days, U leading and r trailing. These delays are consistent with the
existence of a driving source very close to the central supermassive black
hole, which illuminates a standard accretion disk and induces variations
in disk rings at only a few light-days from the massive dark object, i.e.,
at sub-milliarcsecond angles as seen from Earth!

While the central driving source cannot be a standard corona that is emitting the observed
X-rays with a power-law spectrum, a central extreme UV source is the best
candidate to drive the variability of 0957+561. It would be sited just above
the black hole and below the base of the jet perpendicular to the disk.

The GLENDAMA team
plausibly interpret their data as evidence for a power-law X-ray source in
the base of the jet at a typical height of ∼60 light-days. Although the
rapid rotation of the 2.5 thousand million solar mass black hole presumably
disrupts the corona and converts it into a jet, the jet itself would keep a hot
base as a "residual corona". This is a benchmark study to understand the
accretion flow in primeval AGNs displaying jets.